Vitreous compounds with bistable electrical characteristics

ABSTRACT

A new class of vitreous compounds having bistable electrical characteristics, that is to say, two different states of electric resistance is described. The new class of vitreous compounds can be represented by the general formula (1):

United States Patent [1 1 Loriers et al.

[451 Dec. 18, 1973 VITREOUS COMPOUNDS WITH BISTABLE ELECTRICALCHARACTERISTICS [75] Inventors: Jean Loriers, Meudon; Rudolf Heindl,Fontenay Aux Roses, both of France [22] Filed: July 28, 1971 [21] Appl.No.: 166,777

[30] Foreign Application Priority Data July 31, 1970 France 70.28387[56] References Cited UNlTED STATES PATENTS 3,598,762 8/1971 Futaki etal 252/518 2,862,891 12/1958 .lonker et al. 252/518 X 3,258,434 6/1966Mackenzie et al 252/519 3,469,729 9/1969 Grekila ct al. 106/47 R3,503,902 3/1970 Shimoda 252/518 X Primary ExaminerCharles E. Van HornAztorney.1ames and Franklin [57] ABSTRACT A new class of vitreouscompounds having bistable electricalcharacteristics, that is to say, twodifferent states of electric resistance is described.

The new class of vitreous compounds can be represented by the generalformula (1):

2-.r-2z z 2+r+z i-u n 3 12-: 1

1) wherein the letters have the usual meaning of the elements in thePeriodic Table with the exception of Ln which designates as a whole arare earth belonging to the group of lanthanides, such as lanthanum La,or yttrium Y, whereas x, y and 1 each represent numbers between 0 and l,which can separately and simultaneously be zero, which are connected byrelations of ionic equilibrium, and preferablyrespond to theinequalities y 0.5 and z 0.3 An example of compound having the formula(1) is Ca Na Al V 0 (ll) 10 Claims, 3 Drawing Figures VITR-EOUSCOMPOUNDS WITH BISTABLE ELECTRICAL CHARACTERISTICS The object of theinvention is a new class of vitreous compounds having bistableelectrical characteristics, that is to say, two different states ofelectric resistance. It also relates to a process for obtaining same andapplications thereof. 4

Vitreous compounds having such characteristics are already known. It ispossible, for instance, to mention French patents, 1,445,528 and1,351,433 as documents illustrating the prior art in this field. Patent1,445,528 describes binary vitreous compounds. Patent 1,351,433 which isused more particularly as a bibliographical reference in the presentdescription, describes ternary or quaternary vitreous compounds of thetype AsTel, AsTeSe, AsTiSe, VOP, VOPBa, VOPPb or AsBTiO. Suchsemi-conductive compounds are used in electrical elements where they arecombined with an electrical signal source to take advantage of their twostates of resistance at least. Said electric elements are used in thetechnique of switching, in solid state electronic amplifiers andoscillators as well as storage elements, among other things, as theaforesaid French patent explains in detail.

The state of the art with respect to this question can be furtherillustrated by the following documents R. and O. l-lOLZlNGERs articleheaded Feldabhangige Widerstandsanderung in Glasern" in the Germanpublication Zeitschrift fur angewandte Physik, vol. 28, No. 4, 1969,pages 196-201, relating to a vitreous compound for electric devices in aconductive and resistant state, which can comprise and adequate mixtureof B CaO and V 0 oxides.

Swiss patent No. 490,728 (SIEMENS A.G.) relates to a semi-conductiveswitching device without a junction. A vitreous compound is formed froma mixture of V 0 and SrCO United Kingdom Pat. No. 1,168,107 (HITACHILtd.) can also be mentioned it relates to a process for manufacturing athermistor consisting of a sintered mixture of V 0 and a combination ofvarious oxides such as Na, Ca, Al (page 4, example 4), and United StatesPat. No. 3,258,434 assigned to (GENERAL ELECTRIC Co) relating to asemi-conductive glass containing CaO'2B O V O Fe o -Al- O (column 6,example X) as a constituant.

However, the prior art compounds are not satisfactory in all fields ofapplication, and technicians think it desirable to develop vitreouscompounds with, notably, improved mechanical and electrical properties.The object of the present invention is, therefore, vitreous compoundshaving electrical and mechanical properties very superior to those ofsimilar, known compounds.

The new class of vitreous compounds can be represented by the generalformula (1) 2-z-2: 2+1+z t-u ll II IZ-ar -T y O.5 and The chemicalcomposition of the new vitreous compounds appears, at first glance, tobe rather complicated. They all, however, have a common basic matrix offormula (11) Ca Na Al V 0 This particular compound corresponding to theformula (I) wherein x=y=z=0.

The compound of formula (II) has bistable electrical characteristicssuited to the requirements of the invention. Its mechanical andelectrical properties are superior to those of the known compounds. Forexample, the difference in resistivities between the conductive andresistant states is at least 10 times as great as that corresponding tothe prior compounds.

The other compounds of the invention can be obtained from the basicmatrix of formula (ll) by the introduction of the rare earth Ln and/oriron Fe or fluorine F.

In certain cases, bistable glasses can also be obtained by combiningseveral compounds corresponding to formula (I), one of which is, forinstance, the basic compound of formula (ll). The products obtained nolonger correspond to formula (I) but they retain bistable electricalcharacteristics.

A series of examples illustrating said new class of vitreous compoundswill be given hereinafter. The common characteristic of these substancesis that they have bistable electrical characteristics and that they arevitreous, that is to say, they do not show definite lines in X-raydiagrams (Debye-Scherer diagrams). Said new vitreous compounds aremechanically and chemically very stable, contrary to most of the knowncompounds which are very friable and very oxidable glasses containingAs, Te, l or the like.

The new vitreous compounds are prepared under critical conditions forprecursor products of the chemical elements of formula (l), notablyoxides and salts such as carbonates. The mixture of said precursorproducts in substantially stoichiometric proportions corresponding toformula (I) should be heated at high temperature for along period oftime to obtain vitreous compounds.

The invention therefore also relates to a process for obtaining vitreouscompounds corresponding to the aforesaid formula (I) by the intimatecontacting of precursor products with the formation of a mixtureproviding the elements of said compounds in substantially stoichiometricproportions and a thermal treatment, wherein the said mixture is heatedfor at least 5 hours at a temperature higher than 1,300C.

Generally speaking, periods of heating from 6 to 12 hours are suitable,at temperatures of 1,300 to 'l,400C, at 1,350C for example. Melting atinsuffciently high temperatures, or for too short periods of time, doesnot enable vitreous products to be obtained. lf the conditions providedfor in the invention are not respected, products which crystallize oncooling are finally obtained.

The invention will now be illustrated, while in no way being limited bythe following examples EXAMPLE I Preparation of the compound ca wa m V0.

(molecular weight 588.95) There is prepared an intimate mixturecomprising A1 0.5 mole or 50.97 g

CaCO 2 moles or 200.18 g

Na CO 1 mole or 106.00 g

V 0 1.5 mole or 363.8 g

The total weight of the mixture is therefore 720.95 g. The mixture isthen heated open to the air in a platinum crucible at 650C for 2 hours,at 750C for 2 hours and then at 1,350C for 6 hours.

Chemical analyses effected during heating show that the sodium contentdoes not vary.

The product obtained is a vitreous body corresponding to the aforesaidformula (II) and having two different states of electric resistanceElectric measurements were carried out to determine the properties ofthe new product. FIGS. 1 to 3 show the assembly conditions and resultsobtained.

FIG. 1 is a general diagram of the electric circuit permittingvoltage-current characteristics to be obtained.

FIG. 2 is a detailed view showing the assembly of the sample containingproduct (II).

FIG. 3 is the voltage-current curve obtained.

FIG. 1 shows, diagramatically, the assembly used. A continuous 300 voltspower supply 1 is connected to a throw-over switch 2 by a potentiometer3. The throwover switch 2 is connected, on the one hand, to earththrough a resistor 4 or read resistor (100.) and a voltmeter 5, as wellas to the input of a voltage-current curve tracer 6 and, on the otherhand, to sample 7 to be tested through a resistor 8 (501(0). The otherterminal of sample 7 is connected to earth by a resistor 9 and aconductor 10 connects the other input of tracer 6 to one of theterminals of resistor 8.

FIG. 2 shows a detail of the assembly or sample 7.

Two cylindrical graphite pellets, numbered 11 and 12, and between whichis disposed a pellet 13 of the sample of the product to be tested, areinserted between the conductors adapted to connect sample 7 to resistors8 and 9 respectively (FIG. 1). Pellet 13 is maintained between thegraphite cylinders by a conductive coating such as a silver paint put onthe market by the German firm DEGUSSA. Pellet 13 is about 0.1 mm inthickness.

FIG. 3 is the voltage-current curve recorded with the device for sample13 containing compound Ca Na- Al V (II). The voltages are shown inabscissa (volts) and the current in ordinateslmillian aeres) The graphshows that compound (11) has two states: 1. a resistive statecorresponding to values V= 140 V, I=0.l2 m A or R 117 X 10 .0

2. a conductive state corresponding to the values I=4 m A or R 137 X100.

On the curve, portion (A) corresponds to the resistive state and portion(B) to the reducer state.

EXAMPLE 2 which sodium fluoride is incorporated in the amounts 6 given,are subjected to the same thermal treatment as described in example 1.

1.86 mole Ca CO, {86167 g 1.0 mole wa co, 1 106.00 g 0.5 mole A1 0,50.97 g 1.5 mole V 0 363.80 g 0,14 mole NaF 5.88 g Total weight 712.817g A glass having a molecular weight of 586.977 g is obtained.

Formation of glass will not occur with fluoride ion contents higher than0.14.

EXAMPLE 3 To obtain the product Ca Na- Fe V 0 (formula m x 0 y 1 z 0) aswell as the product Ca Na A1 Fe V 0 This latter product, which does notcorrespond to the stoichiometric composition given in formula (I) can beobtained from the basic compound Ca Na A1 V 0 (11) and from the compoundCa Na Fe V3012. I I

3a. The mixture corresponds to the compound Ca Na Fe V3012 0.5 mole Fe;0 79.85 g

and comprises 2.0 moles CaCO 2()() g 1.61m. Na, CO 106.00 g

0.5 mole V 0 272.00 g

Total 657.85 g

W This mixture is heated in a platinum crucible open to the air at 650Cfor 2 hours then at 800C for 2 hours. A reaction product is obtainedwhich is ground fine.

3b. The product (3a) is mixed with 20 moles of product (II) also finelyground. The entire mixture is heated at 1,350C for 6 hours in a coveredplatinum crucible. The glass forms on cooling.

EXAMPLE 4 EiiAMbLES To Obtain the product Ca Y Na V 0, This exampleillustrates a variant of the vitreous comp iti n which can be Ob ed by mx ng a mpou containing yttrium and the basic produce of example 1.

The following mixture is first prepared 0.5 mole Y,O,-, 112.92 g 2.0moles CaCO, 200.00 g 1.0 mole N2i,CO 106.00 g 1.5 moles V,O, 272.00 g

This mixture is heated at 650C for 2 hours and at 800C for 2 hours.

The resulting product is ground. An amount of 0.2

mole (138.18 g) of this finely ground compound is umns of the table thevalues of indices x, y and 2, corresponding to formula (1) are given.The glass formula is given in the fourth column and the amounts in molesand grams of the precursor products used are procedure described inexample 1. In the first three 001- 5 given in the last column, withtheir designation.

. 553 5-- Precursor compounds (amounts in moles and in g) EXAMPLE 6 to24 The following table gives details of a series of glass compositionswhich can be obtained according to the Ex y z Formula Y o 11.29 g. 6 1.111.30 g.

. no... 11.29 g. CO3N212, 111.30 g. 1 11091120. 337.62 g.

La OK. 16.29 g.

La.0 16.29 g.

ZOQ, 11.29 g.

05. 00 N11 111.30 g. 00, 211010.) 911.0, 375.14 g.

0 0.10 0.10ca.,.Ln.,.Na...A1o.,,.1=e..,,v.0,................................. s.00.01.180.16 1;.

05. La Q-pu v.0.

711090 1.. 911.0. 337.62 g. Fe O 7.97 g.

0.12 0.10 0.10 Ca,,mqLn Na, A|1,, Feo, V O F co' ca, 16s.

La o ou Y O O 0.10 Ca sLno oNag.16Al11 sFe1 V O,

La o ou Y O 0.12 0.20 0.10 011mm...1-1a .1., .1=1=.,,.v 0,.1 ....2 COCa, 168.15 g.

3 L e a z a 0.20 0.20 Ca1.1Lno oNa Al6 Fe VOl2............................... CO Ca, 140.12 g.

La O ou Y O lLa O;,, 16.29 g. 11.0., 11.29 g. CO Na 116.6 g. 111010 1.,91-1 0, 300.11 g. v.0..2721s5 Ca gLno uNagiggAlu gFengv o 135F042 CO Ca,Y O ou La O 10, CO Na 116.6 g.

A1(N0.)., 911.0, 300.11 g.

3 g g g 2 g 0 u m u e W. e ..m...

0% .2 2 M m w o MCY .1 e e. 2 91 H a g H g H. & 1 0.z&1.. 2 88%H9 99 g92 92 g .93.HH .O

a 1 7 1 v) \U 3 3) 2 v v 2 pq lvw a aMQM SM MNaMQJ Sa 1w a aflaw .1. 0NO N0 N0 0 3N0 a 0 a N2 (z (z O N wm m n mwmm m mn wmm mmmnm m v .moA ,v...v .00 -v .v .Av .5. bw wem .wfimmmgwmfiimmmwfiem .11110 11 01111 11 11111 01. 10011110 u U m m o. m n n F n F H J m m m m m. m nm N m 1 n O1r 0. u 01 H 3 1 n W v 0 v. w 0. n. o. .6 v 1 v N M w m m V W o M M m n IF 1 1 I .0 0 m M w 1 n 0 L 1| 2 a l a A a 0 m A n a a 1. .N m a a 2 a m6w aw m C C C C C C C 0 0 0 0 0 O 0 0 0 0 1.. l 0O 0 O O O 0 3 0 0 M 0 n0 2 0 4 0 0 0 O 6 7 8 9 W H U TABLE- Continued Ex x y 2 Formula 19 0 021' Ca,,5 Ln},2;NaQMLVQOJ 1.40, CO Ca, 140.12 g.

Precursor compounds (amounts in moles and in g) co caff 2T13'" 0.1.0.,16.29 g. Y.o,, 11.29 g. 1.12. (30.1%,, 118.72 g. I. AI(N0..),,. 911.0.375.14 g. 1 v,o,. 272.85 g.

l 52, 0.12, Y o ou L0 0 1.52, CO -,Ca. 152.13 g.

l a z g 1.1120,, 16.29 g.

5, mo... 7.97 g.

22 Cal,4(lLn0 24Na2 3fiAlojFe0,|VHOH QBFQJZ 1 0, CO Ca, g.

23 0 0.20 0.24 Ca..5.1.11....1 1a A1., ..1=e.,,.v,0,

0.12, La o ou Y O La O 16.29 g.

Y O 11.29 g.

1.12, coma, 118.72 g.

0.9, Al(NO 91-1 0, 337.62 g.

0.05, Fe O 7.97 g.

0.12, FNa, 5.036 g.

.................... 1.52, CO Ca, 152.13 g.

1.12. 00,103,, 1 0.8, A1 No, 911,0, 30011 g. 0.1. n.0,. 15.95 g. 1.5,v,o,, 181.90 g. 0.12, FNa, 5.036 g.

- wherein the letters have the usual meaning of the elements in thePeriodic Table, with the exception of Ln which designates an elementwhich is a part of the group of rare earths belonging to the class oflanthanides and yttrium, whereas x, y and z each represent numbers inthe range of 0 to l, which are bound to-' gether by ionic equilibriumrelationships.

2. The compound of claim 1 wherein x is zero.

3. The compound of claim 1 wherein y is zero.

4. The compound of claim 1 wherein z is zero.

5. The compound of claim 1 wherein x, y and z are simultaneously zero,the said compound corresponding to the formula Ca Na Al V 2 6. Thecompound of claim 1, wherein the element Ln is lanthanum and z isgreater than 0.

7. The compound of claim 1 wherein x, y and z comply with theinequalities wherein the letters have the usual meanings of the ele- 1,300 and 1 ,400C. 65

40 8. A process for the production of a compound of formula (I):

2.r-2z z 2+z+z l-u n V3 u -1 ments in the Periodic Table with theexception of Ln which designates an element which is a part of the groupof rare earths belonging to the class of lanthanides and yttrium,whereas x, y and z each represent numbers in the range of O to l, whichare bound together by ionic equilibrium relationships, said processcomprising the steps, (a) preparation of an intimate mixture ofprecursor products containing the elements of said compound insubstantially stoichiometric proportions, (b) heating said mixture at atemperature higher than about 1,300 C for at least 5 hours and, (c)cooling of said heated mixture to normal temperature, the desiredvitreous compound forming during said cooling.

9. The process of claim 8, wherein the heating (b) is carried out forabout 6 to 12 hours.

10. The process of claim 8, wherein during the heating (b) thetemperature is maintained between about

2. The compound of claim 1 wherein x is zero.
 3. The compound of claim 1wherein y is zero.
 4. The compound of claim 1 wherein z is zero.
 5. Thecompound of claim 1 wherein x, y and z are simultaneously zero, the saidcompound corresponding to the formula : Ca2Na2Al V3O12
 6. The compoundof claim 1, wherein the element Ln is lanthanum and z is greater than 0.7. The compound of claim 1 wherein x, y and z comply with theinequalities x<0.15 y<0.5 and z<0.3
 8. A process for the production of acompound of formula (I): Ca2 x 2zLnz Na2 x z Al1 y Fey V3 O12 xFx (I)wherein the letters have the usual meanings of the elements in thePeriodic Table with the exception of Ln which designates an elementwhich is a part of the group of rare earths belonging to the class oflanthanides and yttrium, whereas x, y and z each represent numbers inthe range of 0 to 1, which are bound together by ionic equilibriumrelationships, said process comprising the steps, (a) preparation of anintimate mixture of precursor products containing the elements of saidcompound in substantially stoichiometric proportions, (b) heating saidmixture at a temperature higher than about 1,300* C for at least 5 hoursand, (c) cooling of said heated mixture to normal temperature, thedesired vitreous compound forming during said cooling.
 9. The process ofclaim 8, wherein the heating (b) is carried out for about 6 to 12 hours.10. The process of claim 8, wherein during the heating (b) thetemperature is maintained between about 1,300* and 1,400*C.